U.S. patent number 5,762,075 [Application Number 08/797,946] was granted by the patent office on 1998-06-09 for method of and apparatus for ascertaining the density of a stream of fibrous material.
This patent grant is currently assigned to Hauni Maschinenbau AG. Invention is credited to Reinhard Hoppe, Henning Moller, Andreas Noack.
United States Patent |
5,762,075 |
Hoppe , et al. |
June 9, 1998 |
Method of and apparatus for ascertaining the density of a stream of
fibrous material
Abstract
The density of a wrapped rod-like filler of tobacco or filter
material for tobacco smoke is ascertained by causing successive
increments of the filler to traverse beams of X-rays which, after
having penetrated through small portions of the filler, impinge
upon detectors forming a linear array and serving to generate
(first) signals denoting the intensities of the respective beams.
Such intensities are affected by the densities of the respective
portions of the filler. The first signals are processed in a
circuit together with one or more additional signals denoting the
intensity or intensities of one or more beams which bypass the
filler, and with one or more further signals furnished by one or
more detectors which are shielded from the source of X-rays. The
thus obtained (second) signal denotes the densities of successive
increments of the filler and is used to correct the density of the
filler, if and when necessary. The processing of first, additional
and further signals in the circuit can involve a summing with or
without preceding logarithmizing, or multiplying of the first
signals and logarithmizing the thus obtained product.
Inventors: |
Hoppe; Reinhard (Tespe,
DE), Moller; Henning (Hamburg, DE), Noack;
Andreas (Hamburg, DE) |
Assignee: |
Hauni Maschinenbau AG (Hamburg,
DE)
|
Family
ID: |
7785497 |
Appl.
No.: |
08/797,946 |
Filed: |
February 12, 1997 |
Foreign Application Priority Data
|
|
|
|
|
Feb 15, 1996 [DE] |
|
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196 05 618.7 |
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Current U.S.
Class: |
131/84.1;
131/281; 131/84.2; 131/84.3 |
Current CPC
Class: |
A24C
5/3412 (20130101) |
Current International
Class: |
A24C
5/34 (20060101); A24C 5/32 (20060101); A24C
005/14 () |
Field of
Search: |
;131/84.1,84.2,84.3,84.4,281,108,905,906 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lewis; Aaron J.
Assistant Examiner: Anderson; Charles W.
Attorney, Agent or Firm: Spencer & Frank
Claims
What is claimed is:
1. A method of ascertaining the density of an advancing flow of
fibrous material of the tobacco processing industry, comprising the
steps of confining the flow to advancement along a predetermined
path; directing beams of X-rays across said path so that said beams
penetrate through different portions of the flow and the intensity
of said beams is influenced by the densities of the respective
portions of the flow; generating first signals denoting the thus
influenced densities of said beams; simultaneously generating at
least one reference signal from said directed beams of X-rays by
directing a portion of said directed beams of X-rays in a direction
which bypasses the advancing flow of fibrous material; and
processing said first signals into a single second signal denoting
the density of the flow, including processing said first signals
with said at least one reference signal.
2. The method of claim 1, wherein said portions of the flow have at
least substantially homogeneous densities.
3. The method of claim 1, wherein said processing step includes
summing of said first signals.
4. The method of claim 1, wherein said processing step includes
logarithmizing and subsequent summing of said first signals.
5. The method of claim 1, wherein said processing step includes
multiplying said first signals and logarithmizing the thus obtained
product of said first signals.
6. The method of claim 1, further comprising the step of generating
at least one dark signal, said processing step including utilizing
said at least one dark signal to compensate for eventual drift of
X-ray detectors which are utilized to generate said first
signals.
7. Apparatus for ascertaining the density of a flow of fibrous
material of the tobacco processing industry which is advanced along
a predetermined path, comprising means for directing beams of
X-rays across a predetermined region of said path so that said
beams penetrate through different portions of an increment of the
flow in said region and the intensities of said beams are
influenced by the densities of the respective portions of the flow;
means for generating first signals denoting the thus influenced
intensities of said beams; means for simultaneously generating at
least one reference signal from said directed beams of X-rays
including means for directing a portion of said directed beams of
X-rays in a direction which bypasses the advancing flow of fibrous
material; and means for processing said first signals and said at
least one reference signal into a single second signal denoting the
density of said increment of the flow.
8. The apparatus of claim 7, wherein said signal generating means
comprises an at least substantially linear array of X-ray
detectors, at least one for each of said different portions of the
increment of the flow in said region of said path.
9. The apparatus of claim 8, wherein said signal generating means
comprises an at least substantially linear array of X-ray
detectors, at least one for each of said different portions of the
increment of the flow in said region of said path, said means for
transmitting said at least one reference signal including an
additional X-ray detector of said array.
10. The apparatus of claim 7, further comprising means for
transmitting to said processing means at least one dark signal
which is utilized to influence said first signals.
11. The apparatus of claim 7, wherein said signal generating means
comprises an at least substantially linear array of X-ray
detectors, at least one for each of said different portions of the
increment of the flow in said region of said path, and further
comprising means for transmitting to said processing means at least
one dark signal which is utilized to influence said first signals
so as to compensate for eventual drifts of said detectors.
12. The apparatus of claim 11, wherein said means for transmitting
said at least one dark signal includes an additional X-ray detector
which is shielded from said directing means.
13. The apparatus of claim 7, wherein said processing means
comprises means for summing said first signals and for converting
the thus generated further signal denoting the sum of said first
signals into said second signal.
14. The apparatus of claim 13, wherein said signal processing means
further comprises means for logarithmizing said first signals prior
to the generation of said further signal.
15. The apparatus of claim 7, wherein said processing means
comprises means for multiplying said first signals to furnish a
further signal denoting the product of said first signals, and
means for logarithmizing said further signal.
16. The apparatus of claim 7, wherein said portions of the
increment in said region of said path have at least substantially
homogenous densities.
17. The apparatus of claim 7, wherein said signal generating means
comprises an at least substantially linear array of X-ray
detectors, at least one for each of said different portions of the
increment of the flow in said region of said path, said array
comprising between 5 and 25 detectors.
18. The apparatus of claim 7, further comprising means for
controlling the density of the flow as a function of the
characteristics of said second signal.
Description
BACKGROUND OF THE INVENTION
The invention relates to improvements in methods of and in
apparatus for ascertaining or determining the density of flows
(such as streams or rods) of fibrous materials, especially those
which are utilized in the tobacco processing industry in connection
with the making of plain or filter cigarettes, cigars, cigarillos
or other rod-shaped smokers' products. The material of the flow can
be natural, reconstituted or artificial tobacco and/or filter
material for tobacco smoke.
Rod making machines for mass production of cigarettes, cigars or
other rod-shaped smokers' products (hereinafter referred to as
cigarettes for short) are normally equipped with apparatus for
continuous monitoring of the density of a flow of fibrous material
prior and/or subsequent to draping of the flow (e.g., a trimmed or
equalized rod-like filler of comminuted tobaco leaf laminae) into a
web of cigarette paper, tipping paper or other suitable wrapping
material. Uniform density as well as a density which at least
closely approximates a predetermined optimum value are very
important criteria which determine the quality (such as the
appearance, the deformability and/or other parameters) of
rod-shaped smokers' products and filter mouthpieces or filter tips
of such products. The density of fibrous material in the tubular
envelope of a plain or filter cigarette or another rod-shaped
smokers' product is indicative of the filling (compactness) of the
product, i.e., of the quantity of fibrous material therein. Among
other influences, the quantity and the uniformity or lack of
uniformity of the distribution of fibrous material in the tubular
envelope determine the resistance which the tobacco filler and the
filter mouthpiece offer to the flow of tobacco smoke
therethrough.
U.S. Pat. No. 4,424,443 (granted Jan. 3, 1984 to Reuland for
"Apparatus for measuring the density of cigarette rods or the
like") discloses an apparatus which employs a source of penetrative
nuclear radiation (such as strontium-90). The radiation is directed
across a moving flow of fibrous material and the extent to which
the intensity of radiation (such as beta rays) is reduced as a
result of penetration through the flow is indicative of the density
of tested increments of the flow. An important advantage of density
measuring apparatus which employ penetrative nuclear radiation is
their reliability, i.e., the density measurements are highly
accurate. However, the utilization of such density measuring
apparatus involves substantial expenditures for safety equipment in
order to properly confine such radiation to the testing
station.
A more recent proposal (disclosed in U.S. Pat. No. 4,805,641
granted Feb. 21, 1989 to Radzio et al. for "Method and apparatus
for ascertaining the density of wrapped tobacco fillers and the
like") involves the utilization of ultraviolet, infrared or visible
light. Such proposal is quite satisfactory as far as the safety of
attendants in the plant for the making of smokers' products is
concerned; however, the reliability of density measurements is not
as high as that of the measurements which are carried out by
resorting to a source of penetrative nuclear radiation.
U.S. Pat. No. 3,056,026 (granted Sep. 25, 1962 to Bigelow for
"Cigarette density gage") proposes to carry out density
measurements by resorting to a source of X-rays. The basic
principle is the same as that involving the utilization of
penetrative nuclear radiation. The beam of X-rays which has
penetrated through the flow of fibrous material is monitored in a
dual ion chamber. The utilization of such chamber limits the rate
at which the density of a moving rod can be ascertained (i.e., the
speed at which the rod can be advanced through the testing
station). Moreover, the resolution (as considered in the
longitudinal direction of a continuous rod to be tested) is rather
unsatisfactory.
A further density measuring apparatus which also relies on X-rays
is disclosed in U.S. Pat. No. 4,785,830 (granted Nov. 22, 1988 to
Moller et al. for "Method and apparatus for monitoring and
evaluating the density of a tobacco stream"). The patent proposes
to direct X-rays through an unwrapped stream or flow of fibrous
material which is confined to advancement within a channel. The
radiation which has penetrated through the stream is monitored by
an array of sensors in order to determine the densities of several
layers of the moving stream, i.e., to separately ascertain the
densities of discrete strata of the advancing flow of fibrous
material. This enables the density measuring apparatus to furnish
signals which are utilized to independently influence the buildup
of the flow of fibrous material, i.e., to vary the density of
fibrous material during the formation of the flow upstream of the
density measuring or monitoring station. The patentees propose to
employ the apparatus for the measurement of density of wrapped or
unwrapped flows of fibrous material; however, no specific
disclosure how to convert or adapt the patented apparatus for the
measurement of density of a rod-like filler which is confined in a
tubular envelope of cigarette paper or the like is actually
disclosed in the patent to Moller et al.
U.S. Pat. No. 4,865,052 discloses an apparatus for the
determination of density of a flow or stream of fibrous material
upstream of a wrapping station. The density monitoring apparatus
employs a source of X-rays which are caused to penetrate across a
stream of tobacco particles in a channel. The characteristics of
the radiation which has pentrated through the unwrapped stream are
monitored by an array of sensors, and the thus obtained signals are
added starting with the signal denoting the density of a layer at
the bottom of the channel. When the sum reaches a predetermined
value, the trimming or equalizing (surplus removing) device
downstream of the density measuring station is adjusted so that it
removes a larger or a smaller quantity of fibrous material from the
advancing stream. This amounts to an advance determination or
selection of the weight (density) of the rod-like filler in the
tubular envelope of the continuous rod which is thereupon
subdivided into cigarettes, cigars, cigarillos or filter rod
sections of desired length. It has been found that such procedure
is not satisfactory in connection with the determination of the
density of successive increments of a rod which is to be subdivided
into a file of plain cigarettes.
To summarize: Density measuring apparatus which employ penetrative
nuclear radiation are reliable and accurate; however, their initial
and maintenance costs are very high. On the other hand, the
presently known density measuring apparatus which operate with
X-rays do not meet the standards expected from a density
measurements particularly in a modern cigarette making machine.
OBJECTS OF THE INVENTION
An object of the invention is to provide a novel and improved
method of ascertaining the density of a moving flow (such as a
rod-like filler in a tubular envelope of cigarette paper or other
suitable wrapping material) by resorting to X-rays.
Another object of the invention is to provide a method which can be
resorted to and can furnish highly accurate and reliable
measurements in connection with the determination of density of
flows containing all types of fibrous materials which are being
processed in connection with the making of various smokable
products with or without filter mouthpieces as well as in
connection with the determination of density of flows of filter
material for tobacco smoke.
A further object of the invention is to provide a relatively
simple, compact, highly reliable and safe apparatus for the
determination of densities of flows of fibrous material of the
tobacco processing industry.
An additional object of the invention is to provide a novel and
improved density measuring apparatus which employs a source of
X-rays.
Still another object of the invention is to provide a density
measuring apparatus which can be installed in existing types of
machines for the making of cigarettes, cigars, cigarillos, cheroots
or filter rods for tobacco smoke.
A further object of the invention is to provide the apparatus with
novel and improved means for processing signals which are
indicative of the densities of various portions of an advancing
flow of fibrous material of the tobacco processing industry.
Another object of the invention is to provide a novel grouping of
detectors for the characteristics of X-rays in an apparatus of the
above outlined character.
SUMMARY OF THE INVENTION
One feature of the present invention resides in the provision of a
novel and improved method of ascertaining the density of an
advancing flow of fibrous material of the tobacco processing
industry (e.g., a stream or filler of shredded and/or otherwise
comminuted tobacco leaves). The method comprises the steps of
confining the flow to advancement along a predetermined path,
directing beams of X-rays across the path so that the beams
penetrate through different portions of the flow and the intensity
of the beams is influenced by the densities of the respective
(irradiated) portions of the flow, generating first signals which
denote the thus influenced intensities of the beams, and processing
the first signals into a single second signal which denotes the
density of the flow.
The portions of the flow which are to be impinged upon by the beams
of X-rays are or can be sufficiently small to ensure that the
density of each such portion of the flow is at least substantially
homogeneous (uniform).
The processing step can include processing the first signals with
at least one reference signal which denotes the intensity of a beam
of X-rays that bypasses the predetermined path, i.e., the intensity
of a beam which was not caused to penetrate through any portion of
the flow. In addition to or in lieu of such processing, the latter
can include a summing or adding of the first signals, particularly
logarithmizing and subsequent summing of the first signals. Still
further, the processing step can include multiplying the first
signals and logarithmizing the thus obtained product of the first
signals.
The method can further comprise the step of generating at least one
dark signal, and the processing step of such method can include
utilizing the at least one dark signal to compensate for eventual
drift of X-ray detectors which are utilized to generate the first
signals.
Another feature of the instant invention resides in the provision
of a novel and improved apparatus for ascertaining the density of a
flow (such as a stream or a rod-like filler) of fibrous material of
the tobacco processing industry which is advanced along a
predetermined path. The apparatus comprises means for directing
beams of X-rays across a predetermined region of the path so that
the beams penetrate through different portions of an increment of
the flow in the aforementioned region of the path and the
intensities of the beams are influenced by the densities of the
respective portions of the flow, means for generating first signals
which denote the thus influenced intensities of the beams, and
means for processing the first signals into a single second signal
denoting the intensity of the tested increment of the flow. The
signal generating means can comprise an at least substantially
linear array of X-ray detectors, at least one for each of the
different portions of the increment of the flow in the
aforementioned region of the path.
The apparatus can further comprise means for transmitting to the
processing means at least one reference signal denoting the
intensity of a further beam of X-rays wich is (or which can be)
furnished by the directing means and bypasses the predetermined
path, i.e., which was not caused to penetrate through the fibrous
material.
The apparatus can also comprise means for transmitting to the
processing means at least one dark signal which is utilized to
influence the first signals, particularly for the purpose of
compensating for eventual drifts of the X-ray detectors. The means
for transmitting the at least one dark signal can include an
additional X-ray detector which is shielded from the directing
means.
The means for processing the first signals can comprise means for
summing or adding the first signals and for converting the thus
generated further signal (denoting the sum of the first signals)
into the second signal. Such signal processing means can further
comprise means for logarithmizing the first signals prior to the
generation of the further signal by the summing means.
It is also possible to employ processing means which comprises
means for multiplying the first signals to furnish a further signal
which denotes the product of the first signals, and means for
logarithmizing the further signal.
As already pointed out above, it is presently preferred to select
the dimensions of the portions of the increment of the flow in the
aforementioned region of the predetermined path in such a way that
their densities are at least substantially uniform
(homogeneous).
By way of example, the aforementioned linear array of X-ray
detectors can comprise between 5 and 25 detectors, particularly
between 10 and 20 detectors.
The processing means can transmit each second signal to suitable
means for controlling the density of the flow as a function of the
characteristics of the second signal.
The novel features which are considered as characteristic of the
invention are set forth in particular in the appended claims. The
improved apparatus itself, however, both as to its construction and
the mode of installing and utilizing the same, together with
numerous additional important and advantageous features thereof,
will be best understood upon perusal of the following detailed
description of certain presently preferred specific embodiments
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic elevational view of an apparatus which
embodies one form of the invention and is positioned to ascertain
the density of successive increments of a rod-like tobacco filler
in a tubular envelope of cigarette paper or other suitable wrapping
material; and
FIG. 2 is a block diagram of the signal processing or evaluating
circuit in the density measuring apparatus of FIG. 1.
DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 illustrates an apparatus which is designed to measure the
densities of successive increments of the rod-like filler 3 of a
continuous cigarette rod 1 having a tubular envelope 2 of cigarette
paper or other suitable material. The rod 1 is assumed to advance
in a direction at right angles to the plane of FIG. 1 within the
confines of a tubular guide 6, at least during advancement through
a density measuring or testing station 4. The rod-like filler 3
within the tubular envelope 2 of the illustrated rod 1 is assumed
to contain tobacco particles of the type utilized for the making of
cigarettes, cigars, cigarillos or cheroots; however, it is equally
possible to utilize the improved apparatus for the determination of
density of successive increments of a continuous rod containing a
rod-like filler of filter material for tobacco smoke.
By way of example, the density measuring apparatus of FIG. 1 can be
installed in a cigarette rod making machine of the type known as
Protos 100 (distributed by the assignee of the present
application). The material of the guide 6 is selected in such a way
that it is permeable to X-rays. For example, the guide 6 can be
made of relatively thin sheet material consisting of aluminum or
titanium. A presently preferred material of the guide 6 is a
polycarbonate, for example MACROLON (Trademark) available at BAYER
AG, or a polyethylene etherketone having a wall thickness in the
range of 0.2 mm. The thickness of the guide 6 which is shown in
FIG. 1 is exaggerated for the sake of clarity, and the illustrated
guide is shown as being made of a metallic material.
A suitable source 7 of X-rays is provided at the station 4 to serve
as means for directing beams 8 of X-rays across a selected
increment of the path for the advancement of the rod 1 and its
filler or flow 3 within the confines of the guide 6. The
representation of the beams 8 as being a set of exactly parallel
rays is a simplified or idealized representation; actually, the
beams 8 are not exactly parallel to each other. Therefore, the
apparatus is provided with two diaphragms 9 and 9a which are
respectively installed upstream and downstream of the guide 6 and
respectively define apertures 11 and 11a for the passage of a set
of beams of X-rays across different portions of successive
increments of the filler 3 in the guide 6. The provision of such
diaphragms has been found to suffice to ensure the traversal of the
filler 3 by a set of beams of X-rays which can be said to be more
or less parallel to each other.
A presently preferred source 7 is an industrial X-ray apparatus
known as Type MF1-30-2 having a normal-focus X-ray tube FK 60-10 W
and being distributed by the Firm Rich. Seifert & Co., D-22926
Ahrensburg, Federal Republic Germany.
The means for measuring the intensity of those beams 8 of X-rays
which have penetrated through different portions of the increment
of the filler 3 at the station 4 includes a receiver 12 which is
located downstream of the aperture 11a of the diaphragm 9a and
comprises a linear array 13 of X-ray detectors 14. Not all of these
detectors are located in the path of beams 8 which have penetrated
across the filler 3 in the guide 6. Depending on the diameter of
the rod 1, the detectors 14.3 to 14.n can be expected to receive
radiation which has passed through the filler 3.
In the apparatus of FIG. 1, n=11, i.e., the total number of
detectors 14 exceeds ten. It has been found that very satisfactory
results can be obtained by utilizing an array 13 which contains
sixteen X-ray detectors 14. Such arrays can be obtained from the
Firm CRYSTAL under the designation Type CXM-HS-03-16K. In FIG. 1,
the character i denotes a number somewhere between 1 and n. Each of
the detectors 14 can have an X-ray sensitive surface with an area
of 1 mm.times.4 mm (as measured vertically and at right angles to
the plane of FIG. 1, respectively). The width of the apertures 11
and 11a can equal or approximate 4 mm, i.e., the same as the width
of radiation-sensitive surfaces of the detectors 14.
In accordance with a feature of the improved density measuring
apparatus, the output of each of the detectors 14.1 to 14.n is
individually connected to the corresponding input of a novel and
improved circuit 16 which evaluates and processes the (first)
signals from those detectors (such as 14.3 to 14.n) located in the
path of beams 8 which have passed through and the intensities of
which were actually influenced by the densities of the
corresponding portions of that increment of the filler 3 which
happens to be located at the station 4. The circuit 16 processes
such (first) signals and transmits a second signal 17 which is
indicative of the density of the respective tested increment of the
filler 3. The signal 17 can be transmitted to a control circuit 18
which either indicates the actual density or which can serve as a
means for directly or indirectly regulating the density of the
filler 3, e.g., by properly adjusting the trimming or equalizing
device which is a standard part of a cigarette rod maker and serves
to remove the surplus from a stream or flow of tobacco particles
which are to be draped into a web of cigarette paper or the like.
Reference may be had, for example, to the aforementioned U.S. Pat.
No. 4,805,641 to Radzio et al. wherein a trimming or equalizing
device is shown in FIG. 1, as at 19.
The array 13 contains at least one detector (shown at 14.2) located
in the path of a beam 8 which has bypassed the filler 3 at the
testing station 4. This detector 14.2 transmits to the
corresponding input of the processing circuit 16 a reference signal
S2, and such signal is processed with signals (such as Sn) denoting
the intensities of beams 8 having passed through that increment of
the filler 3 which happens to be located at the station 4. Though
FIG. 1 shows a single detector (14.2) for the generation of a
reference signal (S2), the apparatus can be designed to furnish to
the processing circuit 16 two or more reference signals, i.e.,
signals generated by those beams 8 which did not penetrate through
fibrous material on their way from the aperture 11 to and beyond
the aperture 11a.
Still further, the array 13 contains at least one detector (shown
at 14.1) which is permanently shielded from the radiation issuing
from the source 7. The detector 14.1 transmits to the corresponding
input of the processing circuit 16 a dark signal S1 which is being
evaluated by the circuit 16 in order to compensate for drift
phenomena in the detectors 14. The quality of the density measuring
action can be enhanced by employing several detectors for the
generation of reference signals (S2) and by employing several
detectors for the generation of two or more dark signals (S1).
The mode of operation of the density measuring apparatus of FIG. 1
will be explained with reference to the block diagram of the
processing or evaluating circuit 16 which is shown in FIG. 2. More
specifically, FIG. 2 illustrates the mode of converting the signals
S1 to Sn from the detectors 14 of the array 13 into the second
signal 17 which is transmitted to the control circuit 18.
The first step involves a calibration of the density measuring
apparatus. To this end, the source 7 of X-rays 8 is turned off or
the diaphragm 9 is closed so that the size of the aperture 11 is
reduced to zero and the receiver 12 is sealed from the source 7.
Thus, each of the signals S1 to Sn from the respective detectors
14.1 to 14.n is a dark signal. The same result can be achieved by
turning the surce 7 off, i.e., this also entails that each of the
detectors 14.1 to 14.n transmits a dark signal corresponding to the
signal S1.
The circuit 16 compares the dark signals from the detectors 14.2 to
14.n with the dark signal S1 from the detector 14.1 (this dark
signal is also called a signal SD for more convenient
identification). The circuit 16 processes the dark signals from the
detectors 14.2 to 14.n into compensation values jD,2 to jD,n, and
such values or data are stored in the memory sections 19.2 to 19.n
of the circuit 16 as constants for use during actual processing of
those first signals S3 to Sn which indicate the densities of those
portions of the filler 3 which were actually traversed by the
respective beams 8 of X-rays. The next step of the calibrating
operation involves the turning on of the source 7, and the
intensities of the beams 8 are evaluated at 14.2 to 14.n prior to
causing a rod 1 to advance in the guide 6 through the density
measuring or testing station 4. Thus, the signals S3 to Sn are then
indicative of the intensities of beams 8 which did not pass through
the filler 3. The thus obtained signals S3 to Sn are reference
signals, the same as the signal S2 (which is a reference signal
also designated as the signal S0). The circuit 16 processes the
signals S2 to Sn (reference signals) to provide reference values
j0,3 to j0,n, and such reference values are stored in the
respective memory sections 21.3 to 21.n of the evaluating circuit
16 as constants.
In order to proceed with a density measuring operation, a rod 1 is
caused to advance through the guide 6 and across the testing
station 4 in a direction at right angles to the plane of FIG. 1.
The radiation source 7 is on so that the beams 8 which are being
propagated toward the detectors 14.3 to 14.n penetrate through the
filler 3 and their intensities are influenced (weakened) to an
extent corresponding to the densities of the respective portions of
the increment of fibrous material then advancing through the
station 4. The detectors 14.3 to 14.n are located in the paths of
propagation of such beams 8 and generate first signals S3 to Sn
which are indicative of the influenced intensities of the
respective beams 8. The processing circuit 16 compares such signals
S3 to Sn with the compensation values jD,3 to jD,n in the
corresponding function units 22.3 to 22.n (i.e., with the dark
signals of the detectors 14.3 to 14.n). The compensation values are
continuously corrected in the calculating stages 24.3 to 24.n as a
function of the then effective or valid dark signal SD from the
continuously shielded X-ray intensity detector 14.1. This results
in a compensation for drift phenomena which might develop in the
detectors 14. For example, such drifting can be the result of aging
of the detectors 14 or it might be attributable to migration of
their thermal characteristics. The comparators 22.3 to 22.n of the
processing circuit 16 transmit to the respective calculating stages
23.3 to 23.n corrected measurement signals S3,k to Sn,k, and such
signals are indicative of the intensities of those beams 8 which
have impinged upon the respective detectors 14.3 to 14.n subsequent
to the passage through the corresponding portions of the increment
of the filler 3 at the testing station 4. In other words, such
signals are indicative of the densities of the respective portions
of the filler 3 at the station 4.
At the same time, the calculating stages 23.3 to 23.n of the
processing circuit 16 receive reference signals I3,k to In,k. Such
reference signals are obtained from the reference values j0,3 to
j0,n which are stored in the memory sections 21.3 to 21.n and are
continuously corrected (in correction stages 25.3 to 25.n) on the
basis of the reference signal S2 (S0) which is supplied by the
detector 14.2, i.e., by the detector which is uninterruptedly
exposed to the action of that beam 8 which bypasses the filler
3.
A correction signal S2,k is generated in the comparator stage 22.2
on the basis of a comparison: (in the stage 24.2) of the reference
value (constant) jD,2 of the signal from the detector 14.2 with the
dark signal SD from the continuously shielded detector 14.1, and
such correction signal S2,k is used in the correction stages for a
correction of the reference values j0,3 to j0,n. In this manner,
the provision of the additional detector 14.2 (which permanently
furnishes a reference signal S2 (S0)), and of the detector 14.1
(which continuously furnishes a dark signal S1 to be used as a
compensating signal) renders it possible to ensure that the density
measurement is not affected by eventual fluctuations of the
intensity of radiation issuing from the source 7, by eventual
drifts of the temperature and/or by eventual aging of the detectors
14.
The corrected measurement signals S3,k to Sn,k are processed in the
calculating stages 23.3 to 23.n with the corrected reference
signals I3,k to In,k to obtain discrete density signals D3 to Dn
each of which is accurately indicative of the density of the
corresponding portion of that increment of the filler 3 which is
located at the testing station 4. This is carried out by
logarithmizing the ratio (quotient) of the reference signal and the
corrected measurement signal. The thus obtained discrete density
representing signals D3 to Dn are transmitted to an adding or
summing stage 26 wherein they are added to form the second signal
17 denoting the density of the respective increment of the filler
3. The signal 17 is transmitted to the control circuit 18 for the
purpose as fully described hereinbefore.
It is also possible to process the signals D3 to Dn into a signal
which is indicative of the average values of such signals and also
denotes the density of the filler 3. The logarithmizing of
individual signals in the stages 23 exhibits (in comparison with
conventional logarithmizing of the integrated density value) the
important advantage that one obtains a mathematically correct (and
hence a more reliable and more accurate) indication concerning the
density of the then irradiated increment of the filler 3 of fibrous
material.
Another possibility of processing the first signals from the
detectors 14.3 to 14.n is to first multiply the quotients of the
reference signals and the corresponding corrected measurement
signals, and to thereupon logarithmize the thus obtained product in
order to obtain the desired second signal 17 indicating the density
of the then monitored increment of the filler 3.
It is preferred to utilize detectors 14 having small or very small
areas which are exposed to X-rays passing through the aperture 11a
of the diaphragm 9a. As mentioned above, it is possible to employ
detectors having radiation-sensitive surfaces in the range of 1 mm
times 4 mm. In other words, each of these detectors generates a
first signal S which is indicative of the density of a very small
portion of the filler 3; this is of advantage because one can
safely assume that the density of each such small portion of the
filler is at least substantially homogeneous (uniform). This, too,
contributes significantly to the accuracy of the second signal 17
which is being transmitted to the control circuit, either for
display or for display and an alteration of the density upstream of
the station 4 or solely for the purposes of density alteration. The
reason is that the logarithmizing of the individual intensity
values constitutes a mathematically correct evaluating step and
reduces or eliminates the likelihood of distortion of the results
of the processing operation. Furthermore, such design of the
detectors renders it possible to achieve a very high
resolution.
It is well known that, during penetration through a mass, the
softer fractions of a radiation are absorbed to a greater extent
than the harder fractions, i.e., a high percentage of the harder
fraction of radiation is likely to penetrate through the mass. This
phenomenon is known as a "hardening" of radiation consisting of
X-rays. It is possible to empirically determine correction factors
for particular types of materials or substances to be exposed to
beams of X-rays, and to use the thus obtained factors to correct
the signals (such as from the detectors 14) in order to account for
the aforementioned hardening of X-rays. This results in a further
improvement of the quality (accuracy and reliability) of the
density measuring operation.
An important advantage of the improved method and apparatus is that
the density of successive increments of a flow of fibrous material
can be ascertained at a rate which is necessary in a machine (such
as a cigarette rod making machine) wherein the filler must be
advanced at an elevated speed, namely at a speed which is required
to turn out well in excess of 10,000 plain cigarettes per minute.
Furthermore, the resolution of the density measurement is highly
satisfactory because one can readily compensate for eventual drift
phenomena in the X-ray detectors as well as for eventual
fluctuations of the radiation (beams 8) issuing from the source
7.
The above outlined highly satisfactory density measurements can be
arrived at by resorting to a suitable source of X-rays rather than
to a source of penetrative nuclear radiation (such as beta rays)
with the aforediscussed attendant problems particularly the
expensive undertakings which are necessary to shield the attendants
from penetrative radiation. In fact, it is possible to design the
source 7 of X-rays in such a way that its dimensions will match
those of a source of penetrative nuclear radiation. In other words,
it is possible to replace a properly designed source 7 of X-rays
for a presently utilized source of beta rays or other penetrative
nuclear radiation.
To logarithmize a given value means to find the logarithm of said
value.
The block diagram of FIG. 2 shows the circuit in a schematic form
for the sake of convenience and simplicity. In actual practice,
e.g., in a cigarette maker, the evaluating circuit preferably
comprises a computer wherein the aforediscussed parts do not
constitute discrete elements but the computer performs the
aforedescribed logarithmizing and other evaluating operations with
the same result.
Without further analysis, the foregoing will so fully reveal the
gist of the present invention that others can, by applying current
knowledge, readily adapt it for various applications without
omitting features that, from the standpoint of prior art, fairly
constitute essential characteristics of the generic and specific
aspects of the above outlined contribution to the art of density
measurement and, therefore, such adaptations should and are
intended to be comprehended within the meaning and range of
equivalence of the appended claims.
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